In recent years, system-on-glass liquid crystal displays are commercially available. These system-on-glass liquid crystal displays have an insulating substrate such as a glass substrate, and driving circuits formed by low-temperature polysilicon thin film transistors (TFTs) and the like are integrated on the insulating substrate. Based on a display with such structure, since driving circuits are directly formed on a glass substrate, the number of external driving ICs can be reduced or the need for such driving ICs can be eliminated. Thus, it is possible to reduce costs, compared with a display on which driving ICs are mounted by a chip-on glass (COG) technique or the like. Generally, such driving circuits formed on the glass substrate of a display are complementary metal oxide semiconductor (CMOS) circuits formed by combining P- and N-channel TFTs.
However, in order to reduce manufacturing costs of such system-on-glass liquid crystal display, it is preferable that driving circuits integrated on the glass substrate be formed by TFTs of a single channel (either N- or P-channel TFTs). Namely, by forming driving circuits with TFTs of a single channel, the number of the manufacturing processes can be reduced, and processes relating to channel characteristics can be reduced by about half, whereby costs can be reduced. For example, Patent Document 1 discloses such single-channel driving circuits.
Further, for a liquid crystal display to be capable of suppressing a driving frequency or changing the scanning direction from top to bottom or bottom to top, the scanning line driving circuits of the display need to have a function of causing scanning lines to be in a floating state. FIG. 3 of Patent Document 2 illustrates an example of the method for causing scanning lines to be in a floating state by using a CMOS circuit. Patent Document 2 uses transmission gates to separate a scanning line and to cause the scanning line to be in a floating state.
Patent Document 1: Japanese Patent Laid-Open No. 2004-226429 (FIG. 1, and the like)
Patent Document 2: Japanese Patent Laid-Open No. 2006-011024 (Table 1, FIG. 2, FIG. 3, and the like)